1. Field of the Invention
The present invention relates to an inkjet printer for printing by ejecting ink on a recording medium.
2. Description of the Related Art
FIG. 13 is a perspective view of a conventional inkjet printer which is shown in part. A reference numeral 1A denotes an ink containing portion where, for example, a replaceable ink cartridge formed of plastic for containing ink is built in a cartridge holder formed of plastic. A reference numeral 1C denotes a driving portion formed of, for example, a piezo element. A reference numeral 1B denotes an ink passage formed of, for example, plastic, for supplying the ink from the ink containing portion 1A to the driving portion 10 on an ink passage. A reference numeral 1D is a nozzle for expelling the ink connected to the driving portion 10 and formed of, for example, metal. A reference numeral 1E is an electrode formed of, for example, aluminum and is evaporated on both sides of a wall surface of the driving portion 10. A reference numeral 1F denotes an external circuit. A control program stored in a storage medium of the external circuit operates a CPU of the external circuit. By supplying the electrode 1E with a control voltage from an external power source which is not shown, a piezo wall of the driving portion 10 having the electrode 1E evaporated on both surfaces thereof, for example, a shaded portion in FIG. 13, is deformed regularly to generate in the driving portion 10 pressure for expelling the ink from the nozzle 1D. The series of operations are driven and controlled.
The ink conventionally used is water-based ink. When the ink jet printer is operated at room temperature, the viscosity of the ink is constant in a range from 5 m Paxc2x7s to 8 m Paxc2x7s. Therefore, it is not necessary to, for the purpose of attaining stable printing quality, adjust the temperature of the ink to control the viscosity of the ink.
In case the ink used in the conventional printer having the above system is oil-based, since the temperature of the ink before printing is started depends on the outside air temperature, the temperature of the ink is low and the viscosity of the ink is high in a low-temperature environment, while the temperature of the ink is high and the viscosity of the ink is low in a high-temperature environment. Therefore, when the ink is oil-based, the viscosity of the ink before the ink is supplied to the driving portion for expelling the ink fluctuates more due to the environmental temperature than a case where the ink is water-based. It follows that, in a case where the ink is oil-based, the range of temperatures where printing is possible with stable printing quality is narrower compared with a case where the ink is water-based.
In view of the above, an object of the present invention is, by heating or cooling the ink to control the temperature of the ink, before the ink flows in the driving portion, to always hold the viscosity of the ink in a state where the printing quality is stable even when the used ink is oil-based ink the viscosity of which varies considerably depending on the temperature of the ink, and, thereby, to widen the range of temperatures where printing is possible with stable printing quality.
In order to solve the above problem, an inkjet printer according to an embodiment of the present invention comprises a heating portion for heating ink, a cooling portion for cooling the ink, a temperature sensor portion for detecting a temperature of the ink, and a control portion for controlling at least one of the heating portion and the cooling portion correspondingly to the temperature detected by the temperature sensor portion to adjust and control the temperature of ink which flow in the driving portion. It is to be noted that the heating portion, the cooling portion, and the temperature sensor portion are provided at a position other than a driving portion for expelling the ink and are directly or indirectly in contact with the ink. This allows the control portion to control at least one of the heating portion and the cooling portion correspondingly to the temperature detected by the temperature sensor portion to hold constant the temperature of the ink before the ink flows in the driving portion. Thus it is possible to hold constant the viscosity of the ink before the ink flows in the driving portion. Therefore, even when oil-based ink is used the viscosity of which varies considerably depending on the environmental temperature, it is possible to widen the range of temperatures where printing is possible with stable printing quality.
In the inkjet printer according to the foregoing embodiment of the present invention, when the temperature of the ink detected by the temperature sensor exceeds an upper limit temperature, the control portion operates the cooling portion to cool the ink, and when the temperature of the ink detected by the temperature sensor exceeds a lower limit temperature which is lower than the upper limit temperature, the control portion operates the heating portion to heat the ink. This allows the temperature of the ink to be held in a range between the upper limit temperature and the lower limit temperature. Thus it is possible to hold constant the viscosity of the ink before the ink flows in the driving portion. Therefore, even when oil-based ink is used the viscosity of which varies considerably depending on the environmental temperature, it is possible to widen the range of temperature where printing is possible with stable printing quality.
In another embodiment of the inkjet printer, when the temperature of the ink detected by the temperature sensor is higher than a reference temperature, the control portion operates the cooling portion to cool the ink, and when the temperature of the ink detected by the temperature sensor is lower than the reference temperature, the control portion operates the heating portion to heat the ink. This allows the temperature of the ink to be held at the reference temperature. Thus it is possible to hold the viscosity of the ink more constant before the ink flows to the driving portion. Therefore, even in case oil-based ink is used the viscosity of which varies considerably depending on the environmental temperature, it is possible to widen the range of temperature where printing is possible with stable printing quality.
In another embodiment of the inkjet printer, when the heating portion is operated, the heating portion is made to generate heat by an electric signal outputted from the control portion to the heating portion and heats the ink, and, when the cooling portion is operated, the cooling portion is made to absorb heat by an electric signal outputted from the control portion to the cooling portion and cools the ink. This allows the temperature of the ink to be controlled in a far shorter time and in a far subtler way before the ink flows in the driving portion as compared with a case of indirect temperature control, using, for example, a water bath, an oil bath, or air cooling. Thus it is possible to easily hold constant the viscosity of the ink before the ink flows in the driving portion. Therefore, even in case oil-based ink is used the viscosity of which varies considerably depending on the environmental temperature, it is possible to widen the range of temperature where printing is possible with stable printing quality.
In another embodiment of the inkjet printer, a maximum value of the upper limit temperature is set to be 60xc2x0 C. or below and a maximum value of the lower limit temperature is set to be 5xc2x0 C. or more or below to the upper limit temperature. This allows the temperature of the ink to be held in a range between the upper limit temperature and the lower limit temperature before the ink flows in the driving portion. Thus it is possible to hold the viscosity of the ink before the ink flows in the driving portion between ink viscosity corresponding to the maximum value 60xc2x0 C. of the upper limit temperature and the maximum value 5xc2x0 C. of the lower limit temperature. It goes without saying that, when the difference between the upper limit temperature and the lower limit temperature is small, the range of fluctuation in the viscosity of the ink becomes small accordingly.
In another embodiment of the inkjet printer, a temperature control range is from 5xc2x0 C. to 60xc2x0 C., the reference temperature is set within the temperature control range such that the viscosity of the ink before the ink flows in the driving portion is in a range between 4 m Paxc2x0s and 20 m Paxc2x0s, and the temperature of the ink is controlled in a range of xc2x15xc2x0 C. with the reference temperature being a center. This allows the temperature of the ink to be held constant at viscosity of the ink corresponding to the reference temperature in the range between 4 m Pa.s and 20 m Paxc2x0s before the ink flows in the driving portion. Therefore, the viscosity of the ink can be adjusted more subtly than in the previous embodiments. It goes without saying that, when the range of xc2x15xc2x0 C. is made narrower with the reference temperature being the center, the viscosity of the ink can be held more strictly constant before the ink flows in the driving portion. Further, it goes without saying that the present claim is also applicable to a case where such ink the viscosity of which does not vary depending on the temperature of the ink is used.
In another embodiment of the inkjet printer, the heating portion, the cooling portion, and the temperature sensor portion are provided at a position other than the driving portion on an ink supply path running from the ink containing portion through the ink passage to the driving portion built in the printing unit so as to be directly or indirectly in contact with ink flowing through the ink supply path. This allows the temperature of the ink to be measured by the temperature sensor before the ink flows in the driving portion. Therefore, the temperature of the ink can be controlled by the control portion using the heating portion and the cooling portion based on the result of the measurement before the ink flows in the driving portion.
In another embodiment of the inkjet printer, the temperature sensor portion is provided at a position in the printing unit other than the driving portion on the ink supply path so as to be directly or indirectly in contact with ink flowing through the ink supply path, and the heating portion and the cooling portion are provided at a position on the ink supply path which is closer to the ink containing portion than the temperature sensor portion. Since the temperature of the ink controlled by the heating portion and the cooling portion is measured just before the ink flows in the driving portion, the temperature of the ink just before the ink flows in the driving portion can be controlled by the control portion using the heating portion and the cooling portion based on the result of the measurement. Therefore, the viscosity of the ink flowing in the driving portion can be held constant even when the ink passage is elongated and the ink containing portion and the printing unit are separated from each other.
In another embodiment of the inkjet printer, the heating portion, the cooling portion, and the temperature sensor portion are provided at a position in the printing unit other than the driving portion on the ink supply path so as to be directly or indirectly in contact with ink flowing through the ink supply path, and the temperature sensor portion is provided at a position which is closer to the driving portion than the heating portion and the cooling portion. This allows the temperature of the ink controlled by the heating portion and the cooling portion to be measured just before the ink flows in the driving portion, and allows, in the vicinity, the temperature of the ink just before the ink flows in the driving portion to be controlled by the control portion using the heating portion and the cooling portion based on the result of the measurement. Therefore, the viscosity of the ink can be held constant more effectively even when the ink passage is elongated and the ink containing portion and the printing unit are separated from each other, since the environmental temperature has almost no influence on the temperature of the ink controlled by the heating portion and the cooling portion.